In the good old days, very few Japanese knew about Alien Registration Cards — you know, those wallet-size documents all non-Japanese residents must carry 24/7 or face arrest and incarceration.
Back then, a "gaijin card" was only something you had to show a bored cop doing random racial profiling on the street.
Legally, in fact, it still is. According to the Foreign Registry Law (Article 13), only officials granted police powers by the Justice Ministry can demand to see one.
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